Noncommutative curves and noncommutative surfaces

In this survey article we describe some geometric results in the theory of noncommutative rings and, more generally, in the theory of abelian categories. Roughly speaking and by analogy with the commutative situation, the category of graded modules modulo torsion over a noncommutative graded ring of quadratic, respectively cubic growth should be thought of as the noncommutative analogue of a projective curve, respectively surface. This intuition has lead to a remarkable number of nontrivial insights and results in noncommutative algebra. Indeed, the problem of classifying noncommutative curves (and noncommutative graded rings of quadratic growth) can be regarded as settled. Despite the fact that no classification of noncommutative surfaces is in sight, a rich body of nontrivial examples and techniques, including blowing up and down, has been developed.Comment: Suggestions by many people (in particular Haynes Miller and Dennis Keeler) have been incorporated. The formulation of some results has been improve

Echo states for detailed fluctuation theorems

Detailed fluctuation theorems are statements about the probability distribution for the stochastic entropy production along a trajectory. It involves the consideration of a suitably transformed dynamics, such as the time reversed, the adjoint, or a combination of these. We identify specific, typically unique, initial conditions, called echo states, for which the final probability distribution of the transformed dynamics reproduces the initial distribution. In this case the detailed fluctuation theorems relate the stochastic entropy production of the direct process to that of the transformed one. We illustrate our results by an explicit analytical calculation and numerical simulations for a modulated two-state quantum dot.Comment: 8 pages, 6 figures, published versio

A mixed elastoplastic / rigid plastic material model

A new integration algorithm for plastic deformation is derived in combination with the\ud anisotropic Hill’49 yield criterion. The algorithm degenerates to the Euler forward elastoplastic material\ud model for small deformations and to the rigid plastic material model for large strain increments. The new\ud model benefits from the advantages of both the elastoplastic and rigid plastic material models: accuracy and\ud fast convergence over a large range of strain increments. The performance of the new algorithm is tested by a\ud deep drawing simulation of a rectangular product. It can be concluded that the new algorithm performs well:\ud the plastic thickness strain distribution of the mixed model inclines towards the elastoplastic material mode

Advanced sheet metal forming

Weight reduction of vehicles can be achieved by using high strength steels or aluminum. The formability of aluminum can be improved by applying the forming process at elevated temperatures. A thermo-mechanically coupled material model and shell element is developed to accurately simulate the forming process at elevated temperatures. The use of high strength steels enlarges the risk of wrinkling. Wrinkling indicators are developed which are used to drive a local mesh refinement procedure to be able to properly capture wrinkling. Besides, to intensify the use of implicit finite element codes for solving large-scale problems, a method is developed which decreases the computational time of implicit codes by factors. The method is based on introducing inertia effects into the implicit finite element code. It is concluded that the computation time is decreased by a factor 5-10 for large-scale problems

New Direct Observational Evidence for Kicks in SNe

We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141-6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).Comment: 2 pages, to appear in the proceedings of the IAU Colloq. 177 "Pulsar Astronomy - 2000 and beyond

Cathodoluminescence of nanocrystalline Y2O3:Eu3+ with various Eu3+ concentrations

© The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.Herein a study on the preparation and cathodoluminescence of monosized spherical nanoparticles of Y2O3:Eu3+ having a Eu3+ concentration that varies between 0.01 and 10% is described. The luminous efficiency and decay time have been determined at low a current density, whereas cathodoluminescence-microscopy has been carried out at high current density, the latter led to substantial saturation of certain spectral transitions. A novel theory is presented to evaluate the critical distance for energy transfer from Eu3+ ions in S6 to Eu3+ ions in C2 sites. It was found that Y2O3:Eu3+ with 1–2% Eu3+ has the highest luminous efficiency of 16lm/w at 15keV electron energy. Decay times of the emission from 5D0 (C2) and 5D1 (C2) and 5D0 (S6) levels were determined. The difference in decay time from the 5D0 (C2) and 5D1 (C2) levels largely explained the observed phenomena in the cathodoluminescence-micrographs recorded with our field emission scanning electron microscope

Improvement of implicit finite element code performance in deep drawing simulations by dynamics contributions

To intensify the use of implicit finite element codes for solving large scale problems, the computation time of these codes has to be decreased drastically. A method is developed which decreases the computational time of implicit codes by factors. The method is based on introducing inertia effects into the implicit finite element code in combination with the use of iterative solvers. Another advantage of introducing inertia effects into an implicit finite element code is that it stabilizes the computation, especially when the problem is under-constrained. The dynamics contributions are successfully implemented for both the plane strain element (only displacement d.o.f.) and the Mindlin shell element (displacement and rotational d.o.f.). Deep drawing simulations are performed to investigate the performance of the dynamics contributions in combination with iterative solvers. It is concluded that the computation time can be decreased by a factor 5–10